Nihil - None; Nothing

Annihilate - v. destroy utterly; obliterate
Nihilistic - adj. rejecting of all religious and moral principles, often in the belief that life is meaningless
Annihilator -n. a person or things that destroy

Nox/ Nec/ Noc - harmful; damaging

Noxious- adj. harmful, poisonous or very unpleasant
Innocuous- adj. not harmful or offensive
Nocuous- adj. noxious, harmful or poisonous